Subject: [PATCH v2 04/12] powerpc/dexcr: Handle hashchk exception

From: Benjamin Gray <[email-masked]>
Date: Thu, 30 Mar 2023 16:50:32 +1100

Recognise and pass the appropriate signal to the user program when a
hashchk instruction triggers. This is independent of allowing
configuration of DEXCR[NPHIE], as a hypervisor can enforce this aspect
regardless of the kernel.

The signal mirrors how ARM reports their similar check failure. For
example, their FPAC handler in arch/arm64/kernel/traps.c do_el0_fpac()
does this. When we fail to read the instruction that caused the fault
we send a segfault, similar to how emulate_math() does it.

Signed-off-by: Benjamin Gray <[email-masked]>

---

v1:	* Refactor the hashchk check to return 0 on success, an error
	  code on failure. Determine what to do based on specific error
	  code.
	* Motivate signal and code
---
 arch/powerpc/include/asm/ppc-opcode.h |  1 +
 arch/powerpc/include/asm/processor.h  |  9 +++++++
 arch/powerpc/kernel/Makefile          |  1 +
 arch/powerpc/kernel/dexcr.c           | 36 +++++++++++++++++++++++++++
 arch/powerpc/kernel/traps.c           | 10 ++++++++
 5 files changed, 57 insertions(+)
 create mode 100644 arch/powerpc/kernel/dexcr.c

diff --git a/arch/powerpc/include/asm/ppc-opcode.h b/arch/powerpc/include/asm/ppc-opcode.h
index 21e33e46f4b8..89b316466ed1 100644
--- a/arch/powerpc/include/asm/ppc-opcode.h
+++ b/arch/powerpc/include/asm/ppc-opcode.h
@@ -215,6 +215,7 @@
 #define OP_31_XOP_STFSX	    663
 #define OP_31_XOP_STFSUX    695
 #define OP_31_XOP_STFDX     727
+#define OP_31_XOP_HASHCHK   754
 #define OP_31_XOP_STFDUX    759
 #define OP_31_XOP_LHBRX     790
 #define OP_31_XOP_LFIWAX    855
diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
index e96c9b8c2a60..bad64d6a5d36 100644
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h
@@ -455,6 +455,15 @@ int exit_vmx_usercopy(void);
 int enter_vmx_ops(void);
 void *exit_vmx_ops(void *dest);
 
+#ifdef CONFIG_PPC_BOOK3S_64
+int check_hashchk_trap(struct pt_regs const *regs);
+#else
+static inline int check_hashchk_trap(struct pt_regs const *regs)
+{
+	return -EINVAL;
+}
+#endif /* CONFIG_PPC_BOOK3S_64 */
+
 #endif /* __KERNEL__ */
 #endif /* __ASSEMBLY__ */
 #endif /* _ASM_POWERPC_PROCESSOR_H */
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index 9bf2be123093..07181e508754 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -88,6 +88,7 @@ obj-$(CONFIG_HAVE_HW_BREAKPOINT)	+= hw_breakpoint.o
 obj-$(CONFIG_PPC_DAWR)		+= dawr.o
 obj-$(CONFIG_PPC_BOOK3S_64)	+= cpu_setup_ppc970.o cpu_setup_pa6t.o
 obj-$(CONFIG_PPC_BOOK3S_64)	+= cpu_setup_power.o
+obj-$(CONFIG_PPC_BOOK3S_64)	+= dexcr.o
 obj-$(CONFIG_PPC_BOOK3S_64)	+= mce.o mce_power.o
 obj-$(CONFIG_PPC_BOOK3E_64)	+= exceptions-64e.o idle_64e.o
 obj-$(CONFIG_PPC_BARRIER_NOSPEC) += security.o
diff --git a/arch/powerpc/kernel/dexcr.c b/arch/powerpc/kernel/dexcr.c
new file mode 100644
index 000000000000..f263e5439cc6
--- /dev/null
+++ b/arch/powerpc/kernel/dexcr.c
@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * DEXCR infrastructure
+ *
+ * Copyright 2023, Benjamin Gray, IBM Corporation.
+ */
+#include <linux/compiler_types.h>
+
+#include <asm/cpu_has_feature.h>
+#include <asm/cputable.h>
+#include <asm/disassemble.h>
+#include <asm/errno.h>
+#include <asm/inst.h>
+#include <asm/ppc-opcode.h>
+#include <asm/ptrace.h>
+#include <asm/reg.h>
+
+int check_hashchk_trap(struct pt_regs const *regs)
+{
+	ppc_inst_t insn;
+
+	if (!cpu_has_feature(CPU_FTR_DEXCR_NPHIE))
+		return -EINVAL;
+
+	if (!user_mode(regs))
+		return -EINVAL;
+
+	if (get_user_instr(insn, (void __user *)regs->nip))
+		return -EFAULT;
+
+	if (ppc_inst_primary_opcode(insn) != 31 ||
+	    get_xop(ppc_inst_val(insn)) != OP_31_XOP_HASHCHK)
+		return -EINVAL;
+
+	return 0;
+}
diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 9bdd79aa51cf..ade67e23b974 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -1516,6 +1516,16 @@ static void do_program_check(struct pt_regs *regs)
 				return;
 			}
 		}
+
+		switch (check_hashchk_trap(regs)) {
+		case 0:
+			_exception(SIGILL, regs, ILL_ILLOPN, regs->nip);
+			return;
+		case -EFAULT:
+			_exception(SIGSEGV, regs, SEGV_MAPERR, regs->nip);
+			return;
+		}
+
 		_exception(SIGTRAP, regs, TRAP_BRKPT, regs->nip);
 		return;
 	}
-- 
2.39.2